If liquid fuel is supplied into the fuel tank of a vehicle including an internal-combustion engine, for example, the occupied volume of the fuel increases in the internal space of the fuel tank. Accordingly, the occupied volume of the gas phase region in the internal space relatively decreases. Thus, the pressure of the gas phase region (hereinafter referred to as a “tank internal pressure”) becomes higher than the atmospheric pressure. As a result, fuel vapor accumulated in the gas phase region of the fuel tank attempts to escape into the atmosphere. If the fuel vapor gas escapes into the atmosphere, the atmosphere is contaminated.
Accordingly, in order to prevent atmospheric contamination caused by escape of the fuel vapor into the atmosphere, conventional fuel tank system has a canister in a vent passage between the fuel tank and the atmosphere. The canister includes an adsorbent that temporarily absorbs the fuel vapor. The absorbent of the canister absorbs the fuel vapor to maintain the tank internal pressure maintained at a low level.
For example, Japanese Patent Application Publication No. 2014-126006 describes an fuel vapor processing device having a seal valve that is provided in a communication passage between a fuel tank and a canister, and that shuts off the fuel tank from atmosphere, a canister, and a diagnosis module that has a leak diagnosis function of an fuel vapor sealing system. The diagnosis module includes a switching valve that opens or closes communication of the canister with the atmosphere, an internal pressure sensor, a flow rate controller that makes the seal valve and the switching valve to be opened and closed, a diagnosis unit that performs leak diagnosis on the fuel vapor sealing system, and a negative pressure pump that generates pressure in the fuel vapor sealing system.
The diagnosis unit of the diagnosis module performs a leak diagnosis on a whole fuel vapor sealing system before a leak diagnosis on the canister section. The diagnosis unit performs a diagnosis function of the seal valve by determining whether a detection value detected by the tank internal pressure sensor varies beyond a predetermined range relative to pressure generated by the negative pressure pump, with the seal valve closed and the switching valve closed.
The fuel vapor processing device according to the Japanese Patent Application Publication No. 2014-126006 performs a diagnosis on function of the seal valve properly.